Steel production generates great amounts of by-products as steel slag. Unlike blast furnace slag, the use of Basic Oxygen Furnace slag (BOF slag) has been restrained due to insufficient volume stability and to the lack of environmental regulations. This study aimed at investigating the potential release and impact of pollutants, especially Cr and V that are present in rather high concentrations in slag, from a BOF slag used in a civil engineering structure (an industrial platform), using a multi-scale approach. The oneyear follow up of the experimental platform showed that concentrations of Cr and V were generally low in seepage waters, and in leachates from leaching test. Microanalyses carried out on slag allowed us to confirm the location of these metals in rather stable ferrous mineral phases, but V was also bound to more reactive silicates. No real toxicity effect of seepage waters has been revealed from eco-toxicological tests carried out with earthworms.
La fabrication de l’acier s’accompagne d’une production d’importantes quantités de co-produits, les laitiers d’aciérie. Contrairement aux laitiers de haut-fourneau, l’utilisation des laitiers d’aciérie de conversion (laitiers LD) a été limitée en raison de leur instabilité volumique et de l’absence de réglementation environnementale. L’objectif de cette étude est d’étudier le relargage potentiel et l’impact des polluants, plus particulièrement de Cr et V qui sont présents à des concentrations assez élevées dans les laitiers, par un laitier LD utilisé dans une structure de génie civil (plateforme industrielle) à l’aide d’une approche multi-échelles.
Evaluation of a full-scale MBBR process for nitrification is reported. Performance of the MBBR was found to be highly dependent on the hydraulic characteristics of the basin which could be optimized with improved influent flow distribution at the basin inlet. Installing a baffle on the influent pipe or introducing influent at multiple points located laterally across the entire influent end of the basin may provide this improvement. Higher aeration (mixing) rates alone did not improve influent distribution, however, increased mixing intensity focused at the inlet was not considered.Laboratory bench-scale analyses were conducted to evaluate the maximum substrate utilization rate, r' m , for the nitrifying biomass in the full-scale MBBR process. Assuming a half-saturation constant, K n , of 1 mg/L, r' m was estimated by statistically fitting the observed data to an attached-growth Monod-type rate expression. Although the data provided an excellent fit, r' m values (20ºC, 8.5 pH) exhibited considerable variation, ranging from 2.024 to 4.418 g/(m 2 -d) with an average of 3.370 g/(m 2 -d). Accurate determination of r' m may be affected by conditions in the full-scale MBBR (e.g. NH 3 -N loading, DO versus NH 3 -N rate limitation, etc.) and/or the assumption that the quantity of active nitrifying biomass is directly related to the media surface area provided. In order to develop a further understanding of the MBBR process, a standardized technique for the determination of r' m is needed.Results of hydraulic analyses indicated that the full-scale MBBR can modeled as two CFSTRs in series with a bypass flow representing hydraulic deficiencies. Model simulations indicated that hydraulic improvement in the full-scale MBBR could significantly increase the design influent NH 3 -N concentration and capacity under NH 3 -N rate limiting conditions. For an MBBR maximized with respect to hydraulic considerations, process performance was found to be highly dependent on r' m . With significant hydraulic deficiencies, process performance is not as sensitive to nitrification kinetics, but rather, is governed by the hydraulic characteristics of the basin.
Submerged attached‐growth processes, both fixed and moving bed, are becoming more popular. These processes may or may not be used in combination with suspended‐growth treatment. The objective of this project was to evaluate a tertiary attached‐growth, moving‐bed media nitrification system based on the ammonia‐nitrogen removal rates and effluent concentrations that could be achieved. A pilot‐scale system for nitrification of secondary municipal wastewater effluent was operated for 142 days. The minimum aeration requirements for media mixing provided sufficient dissolved oxygen. The generation of biological solids from nitrification was insignificant. Design effluent ammonia‐nitrogen concentrations (<6 mg/L) were achieved at influent loading rates greater than design (1.18 g ammonia‐nitrogen/[m2·d]) coincident with detention times shorter than design conditions (4 hours). Empirical relationships for the ammonia‐nitrogen removal rate and effluent concentration as a function of influent ammonia‐nitrogen loading were developed. Detention time is believed to be an important parameter affecting these relationships.
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